Secondary synchronization signal mapping

ABSTRACT

Embodiments of the present disclosure provide a transmitter, a receiver and methods of operating a transmitter or a receiver. In one embodiment, the transmitter is for use with a base station and includes a primary module configured to provide a primary synchronization signal. The transmitter also includes a secondary mapping module configured to provide a secondary synchronization signal derived from two sequences taken from a same set of N sequences and indexed by an index pair (S 1 , S 2 ) with S 1  and S 2  ranging from zero to N−1, wherein the index pair (S 1 , S 2 ) is contained in a mapped set of index pairs corresponding to the same set of N sequences that defines a cell identity group. Additionally, the transmitter further includes a transmit module configured to transmit the primary and secondary synchronization signals.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/974,342 entitled “Secondary Synchronization Signal Mapping” to Eko N.Onggosanusi and Anand G. Dabak filed on Sep. 21, 2007, which isincorporated herein by reference in its entirety.

This application also claims the benefit of U.S. Provisional ApplicationNo. 60/975,062 entitled “Secondary Synchronization Signal Mapping” toEko N. Onggosanusi and Anand G. Dabak filed on Sep. 25, 2007, which isincorporated herein by reference in its entirety.

This application further claims the benefit of U.S. ProvisionalApplication No. 60/975,393 entitled “Secondary Synchronization SignalMapping” to Eko N. Onggosanusi and Anand G. Dabak filed on Sep. 26,2007, which is incorporated herein by reference in its entirety.

This application still further claims the benefit of U.S. ProvisionalApplication No. 60/978,188 entitled “Secondary Synchronization SignalMapping” to Eko N. Onggosanusi and Anand G. Dabak filed on Oct. 8, 2007,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure is directed, in general, to a communicationsystem and, more specifically, to a transmitter, a receiver and methodsof operating a transmitter or a receiver.

BACKGROUND

In a cellular network, such as one employing orthogonal frequencydivision multiple access (OFDMA), each cell employs a base station thatcommunicates with user equipment, such as a cell phone, a laptop, or aPDA, that is actively located within its cell. When the user equipmentis first turned on, it has to do an initial cell search in order to beconnected to the cellular network. This involves a downlinksynchronization process between the base station and the user equipmentwherein the base station sends a synchronization signal to the userequipment.

During initial cell search, the user equipment establishes timing andfrequency offset parameters. Timing involves knowing where to sample thestart of the synchronization frame and associated symbols. Frequencyoffset involves determining the mismatch between the controllingoscillator at the base station and the local oscillator in the userequipment. As the moving user equipment approaches a cell boundarybetween two adjoining cells, it performs a neighboring cell search inpreparation to handover its activation from the initial cell to theneighboring cell. During this time, it receives information from the twobase stations. Improvements in the process of transitioning betweenadjoining cells would prove beneficial in the art.

SUMMARY

Embodiments of the present disclosure provide a transmitter, a receiverand methods of operating a transmitter or a receiver. In one embodiment,the transmitter is for use with a base station and includes a primarymodule configured to provide a primary synchronization signal. Thetransmitter also includes a secondary mapping module configured toprovide a secondary synchronization signal derived from two sequencestaken from a same set of N sequences and indexed by an index pair (S₁,S₂) with S₁ and S₂ ranging from zero to N−1, wherein the index pair (S₁,S₂) is contained in a mapped set of index pairs corresponding to thesame set of N sequences that defines a cell identity group.Additionally, the transmitter further includes a transmit moduleconfigured to transmit the primary and secondary synchronizationsignals.

In another embodiment, the receiver is for use with user equipment andincludes a receive module configured to receive primary and secondarysynchronization signals. The receiver also includes a primary processingmodule configured to detect a partial cell identity from the primarysynchronization signal. Additionally, the receiver further includes asecondary processing module configured to detect a cell identity groupfrom the secondary synchronization signal that is derived from twosequences taken from a same set of N sequences and indexed by an indexpair (S₁, S₂) with S₁ and S₂ ranging from zero to N−1, wherein the indexpair (S₁, S₂) is contained in a mapped set of index pairs correspondingto the same set of N sequences.

In another aspect, the method of operating the transmitter is for usewith a base station and includes providing a primary synchronizationsignal. The method also includes providing a secondary synchronizationsignal derived from two sequences taken from a same set of N sequencesand indexed by an index pair (S₁, S₂) with S₁ and S₂ ranging from zeroto N−1, wherein the index pair (S₁, S₂) is contained in a mapped set ofindex pairs corresponding to the same set of N sequences that defines acell identity group. The method further includes transmitting theprimary and secondary synchronization signals.

In yet another aspect, the method of operating the receiver is for usewith user equipment and includes receiving primary and secondarysynchronization signals. The method also includes detecting a partialcell identity from the primary synchronization signal. The methodfurther includes defining a cell identity group from the secondarysynchronization signal that is derived from two sequences taken from asame set of N sequences and indexed by an index pair (S₁, S₂) with S₁and S₂ ranging from zero to N−1, wherein the index pair (S₁, S₂) iscontained in a mapped set of index pairs corresponding to the same setof N sequences.

The foregoing has outlined preferred and alternative features of thepresent disclosure so that those skilled in the art may betterunderstand the detailed description of the disclosure that follows.Additional features of the disclosure will be described hereinafter thatform the subject of the claims of the disclosure. Those skilled in theart will appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an exemplary diagram of a cellular network employingembodiments a transmitter and a receiver constructed according to theprinciples of the present disclosure;

FIG. 2A illustrates a diagram of a downlink radio frame that includes adownlink synchronization signal constructed according to the principlesof the present disclosure;

FIG. 2B illustrates an embodiment of a primary synchronization signalconstructed according to the principles of the present disclosure;

FIG. 2C illustrates an embodiment of a scrambled secondarysynchronization signal mapping based on employing two segments andconstructed according to the principles of the present disclosure;

FIG. 2D illustrates a diagram of an embodiment of secondarysynchronization sequence scrambling constructed according to theprinciples of the present disclosure;

FIG. 3 illustrates a diagram corresponding to an embodiment of aneighboring cell search as may be employed by user equipment such as theuser equipment discussed with respect to FIG. 1;

FIG. 4 illustrates an embodiment of a segment plane constructedaccording to the principles of the present disclosure;

FIGS. 5A, 5B, 5C and 5D illustrate embodiments of mapping schemes forfirst and second segments of the S-SCH constructed according to theprinciples of the present disclosure;

FIG. 6 illustrates a flow diagram of an embodiment of a method ofoperating a transmitter carried out in accordance with the principles ofthe present disclosure; and

FIG. 7 illustrates a flow diagram of an embodiment of a method ofoperating a receiver carried out in accordance with the principles ofthe present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary diagram of a cellular network 100employing embodiments a transmitter and a receiver constructed accordingto the principles of the present disclosure. In the illustratedembodiment, the cellular network 100 is part of an OFDMA system andincludes a cellular grid having a centric cell and six surroundingfirst-tier cells. The centric cell employs a centric base station BS1,and the surrounding first-tier cells employ first-tier base stationsBS2-BS7, as shown.

The centric base station BS1 includes a first base station transmitter105 and the first tier base station BS2 includes a second base stationtransmitter 115. User equipment (UE) is located on a cell boundarybetween the first and second base station transmitters 105, 115, asshown. The first base station transmitter 105 includes a primary module106, a secondary mapping module 107 and a transmit module 108. Thesecond base station transmitter 115 includes a primary module 116, asecondary mapping module 117 and a transmit module 118. The UE includesa UE receiver 125 having a receive module 126, a primary processingmodule 127 and a secondary processing module 128.

In the first and second base station transmitters 105, 115, the primarymodules 106, 116 are configured to provide a primary synchronizationsignal. The secondary mapping modules 107, 117 are configured to providea secondary synchronization signal derived from two sequences taken froma same set of N sequences and indexed by an index pair (S₁, S₂) with S₁and S₂ ranging from zero to N−1, wherein the index pair (S₁, S₂) iscontained in a mapped set of index pairs corresponding to the same setof N sequences that defines a cell identity group. The transmit modules108, 118 are configured to transmit the primary and secondarysynchronization signals.

In the UE receiver 125, the receive module 126 is configured receiveprimary and secondary synchronization signals. The primary processingmodule 127 is configured to detect a partial cell identity from theprimary synchronization signal. The secondary processing module 128 isconfigured to detect a cell identity group from the secondarysynchronization signal that is derived from two sequences taken from asame set of N sequences and indexed by an index pair (S₁, S₂) with S₁and S₂ ranging from zero to N−1, wherein the index pair (S₁, S₂) iscontained in a mapped set of index pairs corresponding to the same setof N sequences.

FIG. 2A illustrates a diagram of a downlink radio frame 200 thatincludes a downlink synchronization signal constructed according to theprinciples of the present disclosure. The downlink radio frame 200includes two synchronization signals wherein each consists of a primarysynchronization signal (PSS, also termed P-SCH) 205 and a secondarysynchronization signal (SSS, also termed S-SCH) 210 that are located asshown. One PSS 205 and one SSS 210 symbol are transmitted every 5 msepoch. Design of the synchronization signals to enable fast cell search(i.e., less than 100 ms) is required for long-term evolution (LTE) of3GPP.

The underlying code for the PSS 205 is called a primary SYNC code (PSC).The PSC for each cell is chosen from three sequences and is tied to thecell identification (ID) within a certain group of cell IDs. Hence, onePSS symbol carries three cell ID hypotheses. The underlying code for theSSS 210 is called the secondary SYNC code (SSC). The SSS 210 carriescell-specific information. The following cell-specific information maybe carried in one SSS symbol.

As an example, a total of 510 cell IDs are to be supported. Since threecell ID hypotheses are carried in the PSS 205, 170 cell ID groups (170hypotheses) are provided. Additionally, since there are two SSS 210symbols per radio frame 200, a radio framing timing indicator (FT0 orFT1) is also provided. In the illustrated embodiments of the presentdisclosure, two-segment SSC designs may be employed. That is, two groupsof M-sequences with half-length (31) are used to construct a largenumber of composite sequences. Additionally, the two sequences areinterleaved.

The two-segment SSC design inherits problems of ambiguity and collisionin relation to a neighboring cell search. For the case of ambiguity,multiple M-sequences are detected for each of the two SSC segmentsduring the neighboring cell search. For example, if two M-sequences aredetected for each segment, there are a total of four possibilities wheresome may not be valid. Hence, ambiguity occurs when both the SSCsegments corresponding to the two adjacent cells differ. In general, ifn₁ and n₂ M-sequences are detected for segments one and two, there are atotal of n₁×n₂ possibilities (although there are only max(n₁,n₂)distinct cell IDs). For the case of collision, one (and only one) of theSSC segments is identical for several SSC sequences. Essentially, thisamounts to higher pair-wise cross-correlation across the SSC sequences.

FIG. 2B illustrates an embodiment of a primary synchronization signal220 constructed according to the principles of the present disclosure.FIG. 2B shows a mapping in the frequency domain of a PSS correspondingto the primary synchronization signal (PSS) 220 that occupies a center63 sub-carriers, as shown. The mapping also includes a DC sub-carrierand the data sub-carriers. This mapping assumes that there are 31sub-carriers to both the left and right of the DC sub-carrier.

Since coherent SSS detection offers better performance than non-coherentdetection in most scenarios, the PSS and SSS designs accommodateaccurate coherent SSS detection. Additionally, since the PSS is used asa phase reference (to provide channel estimates) for decoding the SSS(demodulating the SSS), the SSS occupies exactly the same set ofsub-carriers as the PSS in the illustrated embodiment.

FIG. 2C illustrates an embodiment of a scrambled secondarysynchronization signal (SSS) mapping 230 based on employing two segmentsand constructed according to the principles of the present disclosure.The SSS mapping 230 occupies the center 63 sub-carriers as discussedwith respect to FIG. 2B. The mapping includes the DC sub-carrier 301 anddata sub-carriers, as before. Here, the mapping shows an interleaving ofsub-carriers representing even and odd scrambled sequences of atwo-segment, interleaved SSS.

In this case, the underlying SSS is of length-31 (two length-31sequences interleaved in the frequency domain). Several naturalcandidates are M-sequences (pseudo noise (PN) sequences), Goldsequences, and truncated Walsh sequences. With Walsh sequences, theunderlying length is 32, with one sample truncated. Other designs arealso possible.

FIG. 2D illustrates a diagram 240 of a construction of the secondarysynchronization signal. The diagram 240 includes first and second SSSsegments as may be employed in subframes 0 and 5 of FIG. 2A above(indicated by m1 and m2, respectively). In subframe 0 (which correspondsto frame timing hypothesis 0), the first SSS segment is provided as aneven sequence, and in subframe 5 (which corresponds to frame timinghypothesis 1), it is provided as an odd sequence, as shown.Correspondingly, in subframe 5, the second SSS segment is provided as aneven sequence, and in subframe 0, it is provided as an odd sequence, asshown. This action causes the swapping of the two SSS sequences insubframes 0 and 5. Each of the even and odd sequences is initiallyscrambled where the scrambling may be the same or different for subframe0 and 5. The resulting even and odd scrambled sequences are interleavedas shown in FIG. 2 c.

FIG. 3 illustrates a diagram corresponding to an embodiment of aneighboring cell search 300 as may be employed by user equipment such asthe user equipment discussed with respect to FIG. 1. The diagram of theneighboring cell search 300 includes user equipment 305 and first andsecond synchronization signals 310, 315.

The ambiguity problem is clearly more detrimental since a wrong cell IDis detected 33 percent of the time. To illustrate the problems moreclearly, different combinations of PSC, SSC1 (segment 1), and SSC2(segment 2) are first identified. Assume a neighboring cell searchscenario in a synchronous network with two cell IDs associated with(PSC, SSC1, SSC2) equal to (Pa, S1a, S2a) and (Pb, S1b, S2b). There areeight possible scenarios, as may be seen in Table 1 below.

TABLE 1 Eight Scenarios for the PSC, SS1 and SSC2 Triplet Scenario Pa &Pb S1a & S1b S2a & S2b Problem 1 Same Same Same n/a 2 Same SameDifferent Collision 3 Same Different Same Collision 4 Same DifferentDifferent Ambiguity 5 Different Same Same — 6 Different Same DifferentCollision 7 Different Different Same Collision 8 Different DifferentDifferent Ambiguity

By further analyzing Table 1 above and employing appropriatedefinitions, the following conclusions may be formed.

-   -   1. When a collision occurs (when only one segment is the same),        ambiguity does not occur since ambiguity requires the two        segments to be different. The converse also holds. Hence,        collision and ambiguity are two disjoint problems).    -   2. Phase mismatch occurs whenever the channel seen by the PSC is        significantly different from that seen by at least one segment        of the SSC. Here, phase mismatch is defined in the context of        the two cells IDs in the neighboring cells.    -   3. Other than the increase in phase mismatch, collision in the        SSC design results in a lower minimum distance for the overall        SSC.    -   4. To avoid a particular ambiguity, the other two cross        combinations are not valid. This is, if the two SSCs are {X1,X2}        and (Y1,Y2) with X1≠Y1 and X2≠Y2, the cross combinations (X1,Y2)        and (X2,Y1) are not allowed to be valid SSCs codes. To fully        avoid ambiguity and collision, there must be a one-to-one        correspondence between segment one and segment two of the SSC.    -   5. Scenario 1 can happen due to a poor or incidental cell ID        assignment for which there is nothing to be done. Scenarios 2,        3, and 4 are typically second-tier interference at best assuming        a reasonable cell ID assignment. Scenarios 5, 6, 7, and 8        correspond to first-tier interference and hence are the most        relevant scenarios.

FIG. 4 illustrates an embodiment of a segment plane 400 constructedaccording to the principles of the present disclosure. The illustratedsegment plane 400 includes lower and upper triangular regions 405, 410corresponding to first and second radio framing timing indicators FT0,FT1. While the region for (S₁, S₂) is illustrated as a plane, the validpoints only include the combinations where S₁ and S₂ are integer between0 and N−1.

Embodiments of this disclosure provide mapping strategies that minimizeboth collision and ambiguity events. Assuming a total of N availableM-sequences per segment, the x-axis and y-axis represent a sequenceindex S₁ and S₂ for segments 1 and 2, respectively. The upper triangularregion 410 is defined as follows: {(S₁,S₂):S₂≧S₁,S_(i)ε{0, 1, . . . ,N−1}}.

The following observations and design principles may be inferred fromFIG. 4.

-   -   1. Ambiguity events can be reduced significantly when a        rectangle mapping region is avoided for a given radio frame        timing hypothesis, since a rectangular mapping ensures the worst        ambiguity condition. For example, if the two SSC mappings are        {X1,X2} and (Y1,Y2) with X1≠Y1 and X2≠Y2, both of the two cross        combinations (X1,Y2) and (X2,Y1) are a valid SSC mapping.    -   2. The number of collision and ambiguity events can be minimized        when all the possible (S1,S2) pairs occupy a region parallel to        the diagonal line of S1=S2 with minimum region width for a given        radio frame timing. This ensures that minimum cross-over with        the horizontal and vertical lines. The principle is analogous to        minimizing the time-bandwidth product of the chirp waveform in        the time-frequency plane. A mapping region as close as possible        to the diagonal line of S1=S2 ensures a minimum region width.        This occurs because the area of the mapping region is maximized.    -   3. With swapped mapping, the mapping only occupies the upper or        lower triangular region of the segment plane 400 for a given        radio frame timing hypothesis    -   4. The design principles in 1, 2, or 3 above can be combined        with other mapping strategies such as the simple or swapped        mapping. With swapped mapping, both the lower and upper        triangular regions 405, 410 are utilized. That is, the mapping        set is partitioned into two parts which are mirror image with        respect to the S1=S2 line. In fact, the combination of swapped        mapping (principle 3) with the diagonal mapping (principle 2)        ensures the minimum region width for a given radio frame timing.

FIGS. 5A, 5B, 5C and 5D illustrate embodiments of mapping schemes forfirst and second segments of the SSS constructed according to theprinciples of the present disclosure. The examples discussed withrespect to FIGS. 5A, 5B, 5C and 5D employ the general structure of FIG.4.

Two radio frame timing hypotheses (FT0 and FT1) and 170 cell group IDsare assumed. This yields a total of 340 hypotheses. Note that thesenumbers are used only for illustrative purposes. For example, thecurrent disclosure also includes a scenario having a different number ofcell identity groups (e.g., 168 cell identity groups). Additionally,N=31 is also assumed.

FIG. 5A depicts a proposed mapping scheme in combination with swappedmapping strategies. In this case, i1, i2, j1, j2 should be chosen suchthat (i2−i1+1)×(j2−j1+1)≧170. Then, a subset of the size-170 can bechosen for each of the two rectangular regions. Each of the tworectangular regions represents one of the two frame timing hypothesesFT0, FT1. The two regions are mirror images of each other with respectto the S1=S2 diagonal line. This mapping scheme, however, results in apoor number of ambiguity events. It may be noted that instead ofoccupying a rectangular region, any arbitrary shape (e.g., triangular oreven circular) can also be used. The rectangular region is only forillustrative purposes.

FIG. 5B depicts a mapping scheme with a triangular mapping region. Inthis case, i1, i2, j1, j2 may be chosen such that

$\frac{\left( {{i\; 2} - {i\; 1} + 1} \right) \times \left( {{j\; 2} - {j\; 1} + 1} \right)}{2} \geq 170.$It may be noted that the embodiments in FIGS. 5A and 5B do notnecessarily follow the second design principle, which will be reflectedin FIGS. 5C and 5D below. Note also that i1, i2, j1, j2 can take anyvalue from 0, 1, . . . , 30.

FIGS. 5C and 5D depict two embodiments that adhere to the second designprinciple, which minimizes the number of collision and ambiguity events.FIG. 5C employs swapped mapping, which is unlike FIG. 5D. For FIG. 5C,i1, i2, j1, j2 is chosen such that

${{\left( {31 - {i\; 2} - {i\; 1}} \right) \times \left( {{i\; 2} - {i\; 1}} \right)} + \frac{\left( {{i\; 2} - {i\; 1}} \right) \times \left( {{i\; 2} - {i\; 1} + 1} \right)}{2}} \geq 170.$Then, a subset of size-170 can be chosen for each of the two stripregions. In this case, a swapped mapping relationship between two SSChypotheses with the same cell ID group holds. For frame timing FT0,(X1,X2) represents the same cell ID group as (X2,X1) for frame timingFT1.

For the example of FIG. 5C, i1, i2, j1, j2 is chosen such that

${{\left( {31 - {i\; 2} - {i\; 1}} \right) \times \left( {{i\; 2} - {i\; 1}} \right)} + \frac{\left( {{i\; 2} - {i\; 1}} \right) \times \left( {{i\; 2} - {i\; 1} + 1} \right)}{2}} \geq 340.$Then, a subset of size-240 can be chosen for each of the two stripregions. In the example of FIG. 5 d, a particular relation for frametiming FT0 and FT1 corresponding to the same cell ID group is notestablished. While FIG. 5D depicts only a lower triangular mappingregion, the same principles may be applied for only an upper triangularmapping region.

Note that i1, i2, j1, j2 (j1 and j2 are directly related by i2 and i1,respectively) can take any value from 0, 1, . . . , 30 although i1=0 isnot preferred for FIG. 5C due to the overlap in the mapping for the twodifferent frame timing instances. To minimize the width of the mappingregion (principle 2), i1=1 is the best choice for both examples of FIGS.5C and 5D. Intuitively, the example of FIG. 5C results in a reducednumber of collision and ambiguity events compared to the other examplesof FIGS. 5A, 5B and 5D.

A final choice of mapping may consider the SSC distance property afterSSC-based scrambling is applied (scrambling of segment 2 as a functionof segment 1). Note that when an M-sequence based SSC is used (all theSSCs are derived from one generator polynomial), the set of scramblingcodes for segment 2 is taken from the same set of codes as segment 1.This is because the resulting set of segment 2 sequences has the maximumset cardinality of 32. Of course, other variations and combinations ofthe above design principles are possible.

In the above examples, it is assumed that the number of cell ID groupsis 170. An extension (or subset) can be used if a larger (or smaller)number of cell ID groups is desired. For instance, if the number of cellID groups is 168 (the one used for LTE), a subset can be used.

Below are two swapped diagonal mapping examples (a first examplecorresponding to Tables 2 and 3 and a second example corresponding toTable 4) along with formulas to generate the code-sequence index forsegment 1 and segment 2. The mapping/pairing (S1,S2) is defined for theone frame timing hypothesis. The pairing for the other frame timinghypothesis is then (S2,S1). An extension (or subset) can be used if alarger (or smaller) number of cell-ID-groups is desired. For example, ifthe number of cell ID groups is 168, the last elements (corresponding toGID=168 and 169 can be discarded).

TABLE 2 Example 1 GID S1 S2 0 0 1 1 0 2 2 0 3 3 0 4 4 0 5 5 0 6 6 1 2 71 3 8 1 4 9 1 5 10 1 6 11 1 7 12 2 3 13 2 4 14 2 5 15 2 6 16 2 7 17 2 818 3 4 19 3 5 20 3 6 21 3 7 22 3 8 23 3 9 24 4 5 25 4 6 26 4 7 27 4 8 284 9 29 4 10 30 5 6 31 5 7 32 5 8 33 5 9 34 5 10 35 5 11 36 6 7 37 6 8 386 9 39 6 10 40 6 11 41 6 12 42 7 8 43 7 9 44 7 10 45 7 11 46 7 12 47 713 48 8 9 49 8 10 50 8 11 51 8 12 52 8 13 53 8 14 54 9 10 55 9 11 56 912 57 9 13 58 9 14 59 9 15 60 10 11 61 10 12 62 10 13 63 10 14 64 10 1565 10 16 66 11 12 67 11 13 68 11 14 69 11 15 70 11 16 71 11 17 72 12 1373 12 14 74 12 15 75 12 16 76 12 17 77 12 18 78 13 14 79 13 15 80 13 1681 13 17 82 13 18 83 13 19 84 14 15 85 14 16 86 14 17 87 14 18 88 14 1989 14 20 90 15 16 91 15 17 92 15 18 93 15 19 94 15 20 95 15 21 96 16 1797 16 18 98 16 19 99 16 20 100 16 21 101 16 22 102 17 18 103 17 19 10417 20 105 17 21 106 17 22 107 17 23 108 18 19 109 18 20 110 18 21 111 1822 112 18 23 113 18 24 114 19 20 115 19 21 116 19 22 117 19 23 118 19 24119 19 25 120 20 21 121 20 22 122 20 23 123 20 24 124 20 25 125 20 26126 21 22 127 21 23 128 21 24 129 21 25 130 21 26 131 21 27 132 22 23133 22 24 134 22 25 135 22 26 136 22 27 137 22 28 138 23 24 139 23 25140 23 26 141 23 27 142 23 28 143 23 29 144 24 25 145 24 26 146 24 27147 24 28 148 24 29 149 24 30 150 25 26 151 25 27 152 25 28 153 25 29154 25 30 155 26 27 156 26 28 157 26 29 158 26 30 159 27 28 160 27 29161 27 30 162 28 29 163 28 30 164 29 30 165 0 7 166 1 8 167 2 9 168 3 10169 4 11 n = GID Define η = round ({square root over (2 × (165 − n)))})Then the mapping is defined as:

TABLE 3 Example 1 n S₁ (n) S₂ (n) 0, 1, . . . , 149 $\frac{n}{6}$ S₁(n) + mod (n, 6) + 1 150, 151, . . . , 164 30 − η S₁ (n) + mod (n + 1,η) + 1, η = 4 S₁ (n) + mod (n, η) + 1, η ≠ 4 165, 166, . . . , 169 n −165 S₁ (n) + 7

TABLE 4 Example 2 GID S1 S2 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 77 8 8 8 9 9 9 10 10 10 11 11 11 12 12 12 13 13 13 14 14 14 15 15 15 1616 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 2424 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 30 30 0 2 31 1 3 32 24 33 3 5 34 4 6 35 5 7 36 6 8 37 7 9 38 8 10 39 9 11 40 10 12 41 11 1342 12 14 43 13 15 44 14 16 45 15 17 46 16 18 47 17 19 48 18 20 49 19 2150 20 22 51 21 23 52 22 24 53 23 25 54 24 26 55 25 27 56 26 28 57 27 2958 28 30 59 0 3 60 1 4 61 2 5 62 3 6 63 4 7 64 5 8 65 6 9 66 7 10 67 811 68 9 12 69 10 13 70 11 14 71 12 15 72 13 16 73 14 17 74 15 18 75 1619 76 17 20 77 18 21 78 19 22 79 20 23 80 21 24 81 22 25 82 23 26 83 2427 84 25 28 85 26 29 86 27 30 87 0 4 88 1 5 89 2 6 90 3 7 91 4 8 92 5 993 6 10 94 7 11 95 8 12 96 9 13 97 10 14 98 11 15 99 12 16 100 13 17 10114 18 102 15 19 103 16 20 104 17 21 105 18 22 106 19 23 107 20 24 108 2125 109 22 26 110 23 27 111 24 28 112 25 29 113 26 30 114 0 5 115 1 6 1162 7 117 3 8 118 4 9 119 5 10 120 6 11 121 7 12 122 8 13 123 9 14 124 1015 125 11 16 126 12 17 127 13 18 128 14 19 129 15 20 130 16 21 131 17 22132 18 23 133 19 24 134 20 25 135 21 26 136 22 27 137 23 28 138 24 29139 25 30 140 0 6 141 1 7 142 2 8 143 3 9 144 4 10 145 5 11 146 6 12 1477 13 148 8 14 149 9 15 150 10 16 151 11 17 152 12 18 153 13 19 154 14 20155 15 21 156 16 22 157 17 23 158 18 24 159 19 25 160 20 26 161 21 27162 22 28 163 23 29 164 24 30 165 0 7 166 1 8 167 2 9 168 3 10 169 4 11n = GID Define $\quad\begin{matrix}{\eta = {{round}\left( \sqrt{2 \times \left( {465 - n} \right)} \right)}} \\{\theta = \frac{\left( {29 - \eta} \right)\left( {30 - \eta} \right)}{2}}\end{matrix}$Then the mapping is defined as

S₁(n) = mod(n − θ, η + 1)${S_{2}(n)} = {{mod}\left( {{S_{1}(n)} + \left\lfloor \frac{n - \theta}{\eta + 1} \right\rfloor + {1,31}} \right)}$

FIG. 6 illustrates a flow diagram of an embodiment of a method ofoperating a transmitter 600 carried out in accordance with theprinciples of the present disclosure. The method 600 is for use with abase station and starts in a step 605. Then, in a step 610, a primarysynchronization signal is provided. A secondary synchronization signalis provided that is derived from two sequences taken from a same set ofN sequences and indexed by an index pair (S₁, S₂) with S₁ and S₂ rangingfrom zero to N−1, wherein the index pair (S₁, S₂) is contained in amapped set of index pairs corresponding to the same set of N sequencesthat defines a cell identity group, in a step 615.

In one embodiment, a first and second frame timing value corresponds toan index pair condition of S₁>S₂ and S₂>S₁, respectively. In anotherembodiment, a first and second frame timing value corresponds to anindex pair condition of S₂>S₁ and S₁>S₂, respectively.

In one embodiment, index pair conditions S₂>S₁ and S₂−S₁ are restrictedthroughout possible integer values by a selected usage of all Nsequences, for a given frame timing value. The indices S₁ and S₂represent two different cyclic shifts of the same M-sequence.Additionally, the number of cell identity groups is 168, N is 31, andthe index pair condition S₂−S₁ ranges from one to seven. Also, indexpair conditions (S₁,S₂)=(m₁,m₂) and (S₁,S₂)=(m₂,m₁) represent a samecell identity group for two different frame timing values. The primaryand secondary synchronization signals are transmitted in a step 620, andthe method 600 ends in a step 625.

FIG. 7 illustrates a flow diagram of an embodiment of a method ofoperating a receiver 700 carried out in accordance with the principlesof the present disclosure. The method 700 is for use with user equipmentand starts in a step 705. Then, in a step 710, primary and secondarysynchronization signals are received. A partial cell identity from theprimary synchronization signal in a step 715. A cell identity group isdefined from the secondary synchronization signal that is derived fromtwo sequences taken from a same set of N sequences and indexed by anindex pair (S₁, S₂) with S₁ and S₂ ranging from zero to N−1, wherein theindex pair (S₁, S₂) is contained in a mapped set of index pairscorresponding to the same set of N sequences, in a step 720.

In one embodiment, a first and second frame timing value corresponds toan index pair condition of S₁>S₂ and S₂>S₁, respectively. In anotherembodiment, a first and second frame timing value corresponds to anindex pair condition of S₂>S₁ and S₁>S₂, respectively.

In one embodiment, index pair conditions S₂>S₁ and S₂−S₁ are restrictedthroughout possible integer values by a selected usage of all Nsequences, for a given frame timing value. The indices S₁ and S₂represent two different cyclic shifts of the same M-sequence.Additionally, the number of cell identity groups is 168, N is 31, andthe index pair condition S₂−S₁ ranges from one to seven. Also, indexpair conditions (S₁,S₂)=(m₁,m₂) and (S₁,S₂)=(m₂,m₁) represent a samecell identity group for two different frame timing values. The method700 ends in a step 725.

While the methods disclosed herein have been described and shown withreference to particular steps performed in a particular order, it willbe understood that these steps may be combined, subdivided, or reorderedto form an equivalent method without departing from the teachings of thepresent disclosure. Accordingly, unless specifically indicated herein,the order or the grouping of the steps is not a limitation of thepresent disclosure.

Those skilled in the art to which the disclosure relates will appreciatethat other and further additions, deletions, substitutions andmodifications may be made to the described example embodiments withoutdeparting from the disclosure.

What is claimed is:
 1. A transmitter for use with a base station,comprising: a primary module configured to provide a primarysynchronization signal; a secondary mapping module configured to providea secondary synchronization signal derived from two sequences taken froma same set of N sequences and indexed by an index pair (S₁, S₂) with S₁and S₂ ranging from zero to N−1, wherein the index pair (S₁, S₂) iscontained in a mapped set of index pairs corresponding to the same setof N sequences that defines a cell identity group, wherein for a givenframe timing value, index pair conditions S₂>S₁ and S₂−S₁ are restrictedthroughout possible integer values by a selected usage of all Nsequences, wherein index pair conditions (S₁,S₂)=(m₁,m₂) and(S₁,S₂)=(m₂,m₁) represent a same cell identity group for two differentframe timing values; and a transmit module configured to transmit theprimary and secondary synchronization signals.
 2. A transmitter for usewith a base station, comprising: a primary module configured to providea primary synchronization signal; a secondary mapping module configuredto provide a secondary synchronization signal derived from two sequencestaken from a same set of N sequences and indexed by an index pair (S₁,S₂) with S₁ and S₂ ranging from zero to N−1, wherein the index pair (S₁,S₂) is contained in a mapped set of index pairs corresponding to thesame set of N sequences that defines a cell identity group, wherein afirst and second frame timing value corresponds to an index paircondition of S₁>S₂ and S₂>S₁, respectively; and a transmit moduleconfigured to transmit the primary and secondary synchronizationsignals.
 3. A transmitter for use with a base station, comprising: aprimary module configured to provide a primary synchronization signal; asecondary mapping module configured to provide a secondarysynchronization signal derived from two sequences taken from a same setof N sequences and indexed by an index pair S₁, S₂) with S₁ and S₂ranging from zero to N−1, wherein the index pair (S₁, S₂) is containedin a mapped set of index pairs corresponding to the same set of Nsequences that defines a cell identity group, wherein a first and secondframe timing value corresponds to an index pair condition of S₂>S₁ andS₁>S₂, respectively; and a transmit module configured to transmit theprimary and secondary synchronization signals.
 4. A method of operatinga transmitter for use with a base station, comprising: providing aprimary synchronization signal; providing a secondary synchronizationsignal derived from two sequences taken from a same set of N sequencesand indexed by an index pair (S₁,S₂) with S₁ and S₂ ranging from zero toN−1, wherein the index pair (S₁,S₂) is contained in a mapped set ofindex pairs corresponding to the same set of N sequences that defines acell identity group, wherein for a given frame timing value, index pairconditions S₂>S₁ and S₁−S₁ are restricted throughout possible integervalues by a selected usage of all N sequences, wherein index pairconditions (S₁,S₂)=(m₁,m₂) and (S₁,S₂)=(m₂,m₁) represent a same cellidentity group for two different frame timing values; and transmittingthe primary and secondary synchronization signals.
 5. A method ofoperating a transmitter or use with a base station, comprising:providing a primary synchronization signal; providing a secondarysynchronization signal derived from two sequences taken from a same setof N sequences and indexed by an index pair (S₁,S₂) with S₁ and S₂ranging from zero to N−1, wherein the index pair (S₁,S₂) is contained ina mapped set of index pairs corresponding to the same set of N sequencesthat defines a cell identity group, wherein a first and second frametiming value corresponds to an index pair condition of S₁>S₂ and S₂>S₁,respectively; and transmitting the primary and secondary synchronizationsignals.
 6. A method of operating a transmitter for use with a basestation, comprising: providing a primary synchronization signal;providing a secondary synchronization signal derived from two sequencestaken from a same set of N sequences and indexed by an index pair(S₁,S₂) with S₁ and S₂ ranging from zero to N−1, wherein the index pair(S₁,S₂) is contained in a mapped set of index pairs corresponding to thesame set of N sequences that defines a cell identity group wherein afirst and second frame timing value corresponds to an index paircondition of S₂>S₁ and S₁>S₂ respectively; and transmitting the primaryand secondary synchronization signals.